1. Field of the Invention
The present invention relates to a pseudo three dimensional (3D) display, i.e., perspective display of a 3D object, and, more particularly, to a depth map generating method and apparatus for generating a depth map of the 3D object, which is used in preparing the perspective display image, from 3D image data that represents the 3D object and is a collection of voxels, elements of 3D structure.
2. Description of the Related Art
There are methods and means for data processing which prepare pseudo 3D images or perspective images from 3D image data of which, like a series of adjoining computed tomography (CT) images, consists of a number of voxels representing a 3D object. The perspective image can be displayed for such analysis and discrimination of the image data as is involved in medical diagnosis.
The perspective image is prepared as follows.
First, for each pixel of a view plane forming a two dimensional (2D) field of view corresponding to the desired view direction, i.e., a projection plane, the distance from the projection plane to the surface of an object is acquired from image data of 3D structure constituted by voxels, then a depth map indicating the distribution of the distance to the object surface in the desired view direction is attained. Then, a predetermined gradation process is executed for assigning gradation like a density value to each pixel of the depth map, thereby preparing the perspective image.
In order to permit an operator to selectively change view directions on a perspective display through his operation, the above process for preparing a depth map must be repeated in an ordinary system every time the view direction is changed.
The generation of a depth map, which can be done using a general-purpose computer, normally takes a significant time, e.g., several tens of minutes since it is necessary to discriminate whether or not an object exists in the view direction for each pixel of a 2D view field for each and every voxel. In order to reduce this processing time, conventional systems often utilize a special-purpose processor that is specifically designed to execute a single type of data processing mentioned above.
Even the conventional systems using such a special-purpose processor require, for example, several seconds. This is still too long to realize true real time processing.